Hybrid impedance matching for inductively coupled plasma system

ABSTRACT

In one aspect, a system includes a generator configured to generate and tune a frequency of a supply signal. The system includes an auto-matching network configured to receive the supply signal and to generate an impedance-matched signal for use in powering a plasma system. In some implementations, during a first stage of an impedance matching operation, the generator is configured to tune the frequency of the supply signal until the generator identifies a frequency for which the reactance of the generator and the reactance of the load are best matched. In some implementations, during a second stage of the impedance matching operation, the auto-matching network is configured to tune a tuning element within the auto-matching network until the auto-matching network identifies a tuning of the tuning element for which the resistance of the generator and the resistance of the load are best matched.

PRIORITY INFORMATION

This application is a Continuation of, and claims priority to, U.S.patent application Ser. No. 13/648,183 (Attorney Docket No.LAMRP002/NVLS003776) by Thomas et al., filed 9 Oct. 2012, and titledHYBRID IMPEDANCE MATCHING FOR INDUCTIVELY COUPLED PLASMA SYSTEM, whichis hereby incorporated by reference herein in its entirety and for allpurposes.

FIELD OF THE INVENTION

The present disclosure relates generally to impedance matching, and morespecifically, to a hybrid impedance matching operation for aninductively coupled plasma system that includes both a frequency tuningoperation as well as an auto-matching operation.

BACKGROUND

An inductively coupled plasma (ICP) system can be used in a variety ofmicrofabrication processes including substrate cleaning processes,surface conditioning processes, thin film deposition processes, etchingprocesses, and cleaning processes, among other applications. In an ICPsystem, a generator supplies a radio frequency (RF) supply signal to aninduction coil. The supply signal generates time-varying magnetic fieldsaround the induction coil that then create electric currents through aprocess gas by way of electromagnetic induction. The electric currentssupply the energy to generate the plasma from the process gas. Animpedance matching network can be used to facilitate the transfer ofpower from the supply signal generator to the induction coil of the ICPsystem and thereby facilitate the formation of the plasma whileminimizing the wasted reflected power and potentially reducing the riskof damage to a device being fabricated in the ICP system as well asdamage to the ICP system components themselves.

SUMMARY

In one aspect of the subject matter described in this disclosure, asystem includes a generator configured to generate a supply signal andto tune a frequency of the supply signal within a tuning range. Thesystem also includes an auto-matching network configured to receive thesupply signal and to generate an impedance-matched signal based on thesupply signal as modified by the impedance of the plasma system and theimpedance of the auto-matching network. A plasma system is configured toreceive the impedance-matched signal. The impedance-matched signalsupplies power to the plasma system for one or more plasma-facilitatedprocesses. In some implementations, during a first stage of an impedancematching operation, the generator is configured to tune the frequency ofthe supply signal until the generator identifies a frequency for whichthe reactance of the generator and the reactance of the load on thegenerator are best matched for the tuning range. In someimplementations, during a second stage of the impedance matchingoperation, the auto-matching network is configured to tune a tuningelement within the auto-matching network until the auto-matching networkidentifies a tuning of the tuning element for which the resistance ofthe generator and the resistance of the load on the generator are bestmatched for the identified frequency.

In some implementations, the generator is configured to generate andoutput the supply signal in forward power mode. In some implementations,the supply signal is a radio frequency (RF) signal. In someimplementations, the generator is configured to generate the supplysignal at frequencies below 1 MHz, and in some such implementations, thegenerator is configured to tune the frequency of the supply signalwithin a range that starts at approximately 380 kHz and which stops atapproximately 440 kHz. In some implementations, to identify thefrequency for which the reactance of the generator and the reactance ofthe load on the generator are best matched, the generator is configuredto identify the frequency of the supply signal for which the generatordetects or determines there is the least power reflected back to thegenerator from the load on the generator. In some implementations, thefirst stage of the impedance matching operation includes a first coarsetuning operation followed by a second fine tuning operation.

In some implementations, the auto-matching network further includes aphase and magnitude detector configured to detect a phase and magnitudeof the supply signal, and to generate phase and magnitude errorcorrection signals based on the detected phase and magnitude. In someimplementations, the phase and magnitude detector is further configuredto detect a phase and magnitude of a signal reflected back from theplasma system. In some implementations, the auto-matching networkfurther includes a controller configured to receive the phase andmagnitude error correction signals, and to generate a tuning signalbased on the phase and magnitude error correction signals. In someimplementations, the tuning element is configured to receive the tuningsignal, which then effects a change in the impedance of the tuningelement based on the tuning signal. In some implementations, the tuningelement is a variable capacitor, and the tuning signal changes acapacitance of the variable capacitor. In some implementations, to tunethe tuning element within the auto-matching network until theauto-matching network identifies a tuning of the tuning element forwhich the resistance of the generator and the resistance of the load onthe generator are best matched, the auto-matching network is configuredto tune the tuning element until one or both of the phase and magnitudeerror correction signals are substantially zero or are below certainthresholds.

In some implementations, the first and second stages of the impedancematching operation are performed in real time. In some implementations,the first and second stages of the impedance matching operation areperformed at each transition between process steps of a multi-stepprocess. In some implementations, the performance of the second stage ofthe impedance matching operation does not begin until the first stage ofthe impedance matching operation identifies the frequency for which thereactance of the generator and the reactance of the load on thegenerator are best matched.

In some implementations, the plasma system is an inductively coupledplasma (ICP) system and the auto-matching network delivers theimpedance-matched signal to an induction coil of the ICP system.

In another aspect of the subject matter described in this disclosure, amethod includes generating, by a generator, a supply signal for use inpowering a plasma system. The method also includes tuning, by thegenerator, a frequency of the supply signal within a tuning range untilthe generator identifies a frequency for which the reactance of thegenerator and the reactance of the load on the generator are bestmatched within the tuning range. The method further includes tuning, byan auto-matching network, a tuning element within the auto-matchingnetwork until the auto-matching network identifies a tuning of thetuning element for which the resistance of the generator and theresistance of the load on the generator are best matched for theidentified frequency. In some implementations, the auto-matching networkis configured to receive the supply signal and to supply animpedance-matched signal to the plasma system, the impedance-matchedsignal supplying power to the plasma system for one or moreplasma-facilitated processes. The impedance-matched signal is based onthe supply signal as modified by the impedance of the plasma system andthe impedance of the auto-matching network including the impedance ofthe tuning element.

In some implementations, the generator is configured to generate andoutput the supply signal in forward power mode. In some implementations,the supply signal is a radio frequency (RF) signal. In someimplementations, the generator is configured to generate the supplysignal at frequencies below 1 MHz. In some such implementations, thegenerator is configured to tune the frequency of the supply signalwithin a range that starts at approximately 380 kHz and which stops atapproximately 440 kHz. In some implementations, tuning a frequency ofthe supply signal until the generator identifies a frequency for whichthe reactance of the generator and the reactance of the load on thegenerator are best matched, comprises tuning the frequency of the supplysignal until the generator detects or determines there is the leastpower reflected back to the generator from the load on the generator. Insome implementations, the tuning of the frequency of the supply signalincludes a first coarse tuning operation followed by a second finetuning operation.

In some implementations, tuning a tuning element within theauto-matching network until the auto-matching network identifies atuning of the tuning element for which the resistance of the generatorand the resistance of the load on the generator are best matched,comprises: detecting one or both of a phase and a magnitude of thesupply signal; generating one or more phase error corrections signalsand/or one or more magnitude error correction signals based on thedetected phase and magnitude; and generating a tuning signal for tuningthe tuning element based on one or both of the phase and magnitude errorcorrection signals. In some implementations, the tuning element isconfigured to receive the tuning signal, which then effects a change inthe impedance of the tuning element based on the tuning signal. In someimplementations, the tuning element is a variable capacitor, and whereintuning the tuning element with the tuning signal comprises changing acapacitance of the variable capacitor. In some implementations, tuningthe tuning element within the auto-matching network until theauto-matching network identifies the tuning of the tuning element forwhich the resistance of the generator and the resistance of the load onthe generator are best matched comprises tuning the tuning element untilone or both of the phase and magnitude error correction signals aresubstantially zero or are below certain thresholds.

In some implementations, the tuning of the frequency of the supplysignal by the generator and the tuning of the tuning element by theauto-matching network are performed in real time. In someimplementations, the tuning of the frequency of the supply signal by thegenerator and the tuning of the tuning element by the auto-matchingnetwork are performed at each transition between process steps of amulti-step process. In some implementations, the tuning by theauto-matching network does not begin until the tuning of the frequencyof the supply signal results in the identification of the frequency forwhich the reactance of the generator and the reactance of the load onthe generator are best matched.

In some implementations, the method further includes performing anetwork analysis operation to identify one or more resonance points thatshould not be tuned to or tuned over during the tuning of the frequencyof the supply signal. In some implementations, the plasma system is aninductively coupled plasma (ICP) system and wherein the auto-matchingnetwork delivers the impedance-matched signal to an induction coil ofthe ICP system.

These and other aspects are described further below with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an example inductively coupledplasma (ICP) system suitable for use in conjunction with variousembodiments.

FIG. 2 shows a block diagram depiction of an example ICP system suitablefor use in conjunction with various embodiments.

FIG. 3 shows a flowchart illustrating an example impedance matchingprocess.

FIG. 4 shows a flowchart illustrating an example initialization andsynchronization process.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the presented embodiments.The disclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

An inductively coupled plasma (ICP) system can be used in a variety ofsemiconductor device fabrication and other microfabrication processesincluding substrate cleaning processes, metal cleaning processes,surface conditioning processes, thin film deposition (e.g., sputtering)processes, etching (e.g., reactive-ion etching) processes, and chambercleaning processes, among other applications. For example, an ICPsystem-generated plasma can be used to clean a substrate prior todeposition of a tungsten nucleation layer or to remove metal oxide frommetal contacts. FIG. 1 shows a schematic depiction of an example ICPsystem 100 suitable for use in conjunction with various embodiments. TheICP system 100 includes a reaction chamber 102 in which the plasma isgenerated and in which the fabrication, cleaning, or otherplasma-enhanced or plasma-facilitated processes are performed. In someembodiments, the reaction chamber 102 is surrounded by a hemisphericdome 104. In some such implementations, the hemispheric dome 104 can beformed of a ceramic material. An induction coil 106 is wound outside thedome 104. For example, the induction coil can be formed of copper oranother highly conductive material. In some implementations, the coil ishollow allowing for the passage of a coolant such as water within thecoil.

The induction coil 106 is supplied by a generator 108. In someimplementations, the generator 108 is a medium frequency RF (MFRF)generator. The medium frequency range generally refers to radiofrequencies in the range of 300 kilo-Hertz (kHz) to 1 Mega-Hertz (MHz).During operation, the generator 108 generates an RF alternating current(AC) supply signal that is supplied to the induction coil 106. In someimplementations, the generator 108 is configured to generate a supplysignal having a frequency below approximately 2 MHz, and in some evenmore specific implementations, below 1 MHz. In some specificapplications, the generator 108 is configured to generate a supplysignal having a frequency in the range of approximately 330 kHz toapproximately 460 kHz. The generator 108 delivers the supply signal tothe induction coil 106 via an impedance matching network 110, asdescribed further below with respect to FIGS. 2-3. Additionally, in someembodiments, the ICP system 100 can include a plurality of inductioncoils, each of which may be connected to a different generator by way ofa different matching network.

Within the reaction chamber 102, a wafer pedestal 112 supports asubstrate 114. For example, the substrate 114 can be a semiconductorwafer or a glass or other dielectric substrate. The pedestal 112typically includes a chuck (sometimes referred to as a clamp) to holdthe substrate 114 in place during processing. The chuck may be anelectrostatic chuck, a mechanical chuck or various other types of chucksuitable for use in the industry and/or research. A heat transfersubsystem including a line 115 for supplying heat transfer controls thetemperature of substrate 114. The wafer chuck and heat transfer systemcan facilitate maintaining the appropriate wafer or other substratetemperatures.

In some implementations, the ICP system 100 additionally includes a highfrequency RF (HFRF) generator 116. For example, the HFRF generator 116can be used to electrically bias the substrate 114. Additionally, theHFRF generator 116 can be used to draw charged species to the substrate114 during one or more process steps. Electrical energy from the HFRFgenerator 116 can be supplied to the substrate 114 via an electrode orthrough capacitive coupling, for example. In some other implementations,the generator 116 can be configured to supply a bias in anotherfrequency range less than or greater than RF frequencies. In some otherimplementations, the generator 116 can be configured to supply a DCbias.

During operation, one or more process gases, such as argon (Ar),hydrogen (H), or nitrogen (N), among other examples, are introduced viaone or more inlets 118. It is the process gas or gases that will betransformed to the plasma state of matter by the ICP system 100. Invarious applications, the process gases may or may not be premixed. Insome implementations, the process gases can be introduced through a gassupply inlet mechanism including orifices. Some of the orifices canorient the process gas or gases along an axis of injection intersectingan exposed surface of the substrate 114 at an acute angle. In some otherimplementations, the gas or gas mixtures can be introduced from aprimary gas ring 120. In various applications, the gas ring 120 candirect the gas toward the surface of the substrate 114. For example,injectors can be connected to the primary gas ring 120 to direct atleast some of the gas or gas mixtures into the chamber 102 and towardthe substrate 114. In some implementations, process gases exit thechamber 102 via an outlet 122. A vacuum pump (e.g., a turbomolecularpump) typically draws process gases out and maintains a suitably lowpressure within the reaction chamber 102.

In one example of a plasma-facilitated process step, the ICP system 100is configured to pre-treat a semiconductor wafer substrate 114. Forexample, the semiconductor wafer substrate 114 can include a hole in adielectric layer exposing a nickel (Ni) or other metal contact. Such apre-treatment can be performed prior to deposition of a tungstennucleation layer in the hole. In one example implementation of anICP-facilitated multi-step pre-treatment, the ICP system 100 isconfigured to perform four process steps or phases: (1) ignition of theplasma using an Ar gas flow; (2) cleaning or removing the oxide on theNi contact using a combined Ar and hydrogen (H₂) flow; (3) enhancingadhesion to the dielectric hole sidewall using a combined nitrogen (N₂)and H₂ flow; and (4) extinguishing of the plasma.

Each transition from one process step, phase or stage to the next canand generally does cause the impedance of the load on the generator 108to change. By way of background, the impedance Z can be a complex numberhaving a real component (the resistance) and an imaginary part (thereactance). For example, the impedance can be written in Cartesian formas

Z=R+jX,

where R is the resistance and X is the reactance. Thus, each transitionfrom one process step or stage to the next can cause both the resistanceand the reactance of the load on the generator 108 to change. Indeed,any change in any of the power or frequency of the supply signal, anychanges in the gases flowing in the chamber 102, or other changes in thereaction chamber 102 will generally cause a change in one or both of theresistance and the reactance of the load. Generally, an impedancematching network is used to match the impedance of the source Z_(S) tothe impedance of the load Z_(L).

Embodiments of the present disclosure relate to an impedance matchingnetwork for maximizing the power transfer from a source, such as thegenerator 108, to a load, such as the induction coil 106 and other ICPsystem 100 components including the process gas or gases. Although theinvention is not limited to embodiments that utilize a system such asthe ICP system 100 described and illustrated with reference to FIG. 1,for convenience of describing example embodiments in the followingdescription, reference may be made generally to the components of ICPsystem 100. Maximum power transfer from the source to the load isachieved when

Z _(S) =Z _(L)*,

where Z_(L)* is the complex conjugate of Z_(L). The impedance matchingnetwork also can minimize reflections from the load. Minimum reflectionis achieved when

Z _(S) =Z _(L).

The impedance matching network 110 is disposed between the generator 108and the induction coil 106 and, at a high level, is configured to matchan impedance of the load the supply signal drives with an impedance ofthe generator 108 that generates the supply signal. As described above,the impedance of the load includes, for example, impedance contributionsfrom the induction coil 106, the gas flowing in the chamber 103, and theimpedance from the matching network 110 itself, among other possiblecontributions, some or all of which are dependent on the frequency andpower level of the supply signal from the generator 108. The matchingnetwork 110 ideally functions to compensate for the difference betweenthe resistance of the generator 108 and the resistance of the load, andto compensate for the difference between the reactance of the generator108 and the reactance of the load.

Traditionally, impedance matching networks include elements such ascapacitors. So-called auto-matching networks include tuning elementssuch as, for example, variable vacuum capacitors. Auto-matching networksideally adjust their own resistance and reactance by way of varying thecapacitance of a capacitor in response to a feedback signal such thatthe impedance of the combined load—with the matching networkconnected—is the complex conjugate of the impedance of the source—thegenerator. Generally, the size of the components, especially thecapacitors, required for a given supply signal frequency is inverselyproportional to the frequency. So, as lower frequencies are desired forcertain processes, the components required generally must be large. Onereason for this is because ICP generators operating at low or mediumfrequencies also typically generate high voltages. For example, low ormedium frequency processes can include cleaning processes that useparticular species so as to avoid damage to the substrate or devicesfabricated or to be fabricated on the substrate. To accommodate the highvoltages, traditional ICP systems require components rated for both highvoltages and rated for low or medium frequencies. Generally, capacitorshaving high capacitances are required for such applications.Commercially, it is difficult to produce variable vacuum capacitors thatcan operate at low or medium frequencies, such as below 1 MHz, and morespecifically at around approximately 400 kHz, with the high capacitancesrequired because of the size generally required of such devices. Thus,traditionally, fixed impedance matching networks have been used with lowor medium frequency ICP generators. In contrast, at frequencies above,for example, approximately 2 MHz, variable impedance auto-matchingnetworks have been utilized.

Because the impedance of a fixed matching network is fixed, it can onlyprovide the best impedance matching for one particular load impedance,and hence for one process step “recipe” (e.g., including the power andfrequency of the supply signal, the gas mixture, the gas flow rate, thetemperature, the pressure, and/or other specified conditions in thereaction chamber). However, in multi-step process flows, as theimpedance of the load changes from the one process step for which thefixed impedance matching network is designed to a different process stepor condition having a different impedance, the power transfer from thegenerator to the induction coil is reduced and the reflected powerincreases. Some traditional fixed matching networks are configured tomatch to an impedance value between the impedance values associated withtwo different process steps. While this may provide a coarse solutionfor certain applications, the power reflected during each of the twoprocess steps is often too much for other applications. Additionally,some applications may require three or more process steps, each of whichmay have a different recipe, making such traditional solutions even lesseffective. Additionally, there are also transient voltage and powerspikes associated with the transition between process steps or phases;that is, in addition to the power reflected as a result of asteady-state impedance mismatch. For example, even in single processstep applications, there are power spikes in igniting the plasma and intransitioning from the plasma ignition phase to a steady-state processstep phase. In addition to wasting energy and possibly damaging thegenerator or other ICP system components, power spikes can result indamage to the substrate and any devices fabricated or to be fabricatedon the substrate.

Additionally, ICP system generators are typically designed to operate atcertain impedances—for example, 50 Ohms (Ω). However, because theimpedance of the generator also is generally a function of one or bothof the frequency of the supply signal and the power in the supply signalthe generator 108 is supplying, ICP generators running at low or mediumfrequencies, such as around approximately 400 kHz, may not operate at50Ω. As a result, when an ICP system transitions from plasma ignition toa steady-state flow or as the ICP systems transitions through variousprocess steps or phases of operation, such as the ICP-facilitatedmulti-step pre-treatment described above, there can be impedance changeson both the source (generator) side and the load side resulting in thedevelopment of high voltages and power spikes.

In summary, because traditional ICP systems that operate at low ormedium frequencies (e.g., less than 2 MHz in some implementations, lessthan 1 MHz is some more specific implementations, and in the range ofapproximately 330 kHz to approximately 460 kHz in some even morespecific implementations) require large capacitors and other components,and because variable versions of such components are not commerciallyavailable, fixed matching networks have traditionally been used. Becausefixed matching networks are only able to match the source impedance tothe load impedance for one limited system impedance, such fixed matchingnetworks can only offer suitably low reflected power for a small loadimpedance range. Generally, the reflected power increases and thepercentage of power delivered to the induction coil for a given powersupplied by the generator decreases as the impedance mismatch betweenthe source and the load increases. Thus, traditional ICP systemstypically run in delivered-power mode to ensure that enough power isdelivered to the induction coil to meet the process step requirements.In delivered-power mode, the generator delivers the same power in thesupply signal to the induction coil regardless of the power reflectedand detected by the generator. For example, to supply the power for aprocess that requires 2000 Watts (W), a generator in delivered powermode may have to supply significantly more than 2000 W. Morespecifically, because of an impedance mismatch between the generator andthe load, the load may be reflecting, for example, 500 W, thus requiringthe generator to output 2500 W in delivered power mode to compensate forthe 500 W of reflected power. However, although the required power mayactually be delivered to the load, as described above, at low or mediumfrequencies, particularly around 400 kHz, the transient power spikes andvoltages at transition points between process steps can cause damage tothe substrate or devices fabricated on the substrate as well as to thegenerator or other components of the ICP system.

In contrast, in forward power mode, the generator outputs a steady fixedpower supply signal V_(S) regardless of the power reflected. Thus, agenerator that, for example, outputs 2000 W in forward power mode, ofwhich 200 W (10%) is reflected, only delivers 1800 W to the ICP system.Currently there does not exist a commercially available auto-matchingnetwork for an ICP generator operating at low or medium frequencies inforward power mode that can keep the reflected power low enough to meetvarious specification requirements. For example, some devicemanufacturers desire that the reflected power stays under 2%—forexample, less than 30 W reflected power for a 2000 W forward powersupply signal—for every process step and during the transitions betweenprocess steps. However, typical reflected power measurements are in therange of approximately 5% to 10% or higher for traditional ICP systemsgenerating low or medium frequency supply signals. Additionally,transient conditions can result in sharp increases in the reflectedpower and in power spikes delivered to the ignition coil.

Various embodiments utilize one or more tuning elements in anauto-matching network as well as the frequency tuning capabilities of anICP generator to perform a two-stage impedance matching operation. Morespecifically, various embodiments advantageously utilize the frequencytuning (or dithering) capabilities of the ICP generator 108 to adjustthe reactance the imaginary part of the impedance (the frequency tuningmay in some instances also affect the resistance). Various embodimentsalso advantageously utilize the tuning element(s) in an auto-matchingnetwork 110 to adjust the resistance—the real part of the impedance (theauto-matching network may in some instances also affect the reactance).Another aspect of the present disclosure concerns synchronizing thefrequency tuning operations of the generator 108 with the capacitive (orother) tuning capabilities of the auto-matching network 110.

FIG. 2 shows a block diagram depiction of an example ICP system 200suitable for use in conjunction with various embodiments. The ICP system200 includes an ICP plasma chamber 202 including a conduction coil 206.The ICP system 200 further includes a medium frequency RF generator 208configured to generate a supply signal V_(S) and to tune a frequency ofthe supply signal V_(S) within a range of frequencies. In someparticular embodiments, the generator 208 is configured to generate asupply signal V_(S) having a frequency within a range of approximately330 kHz to approximately 460 kHz. The generator 208 is configured tooutput the supply signal V_(S) in forward power mode; that is, at afixed output power. An auto-matching network 210 receives the supplysignal V_(S) and delivers an impedance-matched signal V_(L) to theinduction coil 206. The generator 208 is further configured to detect(or otherwise determine based on one or more sensors or other feedbackmechanisms) the forward power output from the generator as well as thepower reflected back to the generator from the load. In someimplementations, the generator 208 can have its own control loop thatenables it to detect the power output from the generator as well as thepower reflected back to the generator.

In some embodiments, the auto-matching network 210 includes a phase andmagnitude detector 224 that is configured to detect a phase and amagnitude (e.g., voltage and/or power) of the forward power supplysignal V_(S) before passing the supply signal to a tuning element 226within the auto-matching network. In some embodiments, the phase andmagnitude detector is further configured to detect the phase andmagnitude (e.g., voltage and/or power) of any signals reflected from theinduction coil 206. In some example implementations, the phase andmagnitude detector 226 is configured to sample the supply signal V_(S)and any reflected signals at a sampling frequency in the range ofapproximately 100 Hz to 1 kHz. The phase and magnitude detector 224sends phase and magnitude error correction signals to a controller 228.Based on the phase and magnitude error correction signals, thecontroller 228 generates and sends a tuning signal to the tuning element226. The tuning signal causes one or more characteristics of the tuningelement 226 to change in order to effect a change in the impedance ofthe auto-matching network 210 such that the impedance of the load on thegenerator 208 is matched as closely as possible to the impedance of thegenerator 208. In some implementations, as described below, the tuningelement 226 of the auto-matching network is configured to only, orprimarily, effect a change in the real part of the impedance—theresistance. In some implementations, when the phase and magnitude errorcorrection signals are zero the impedance, or at least the resistance,of the load is fully matched to the impedance of the generator 208. Insome implementations, the tuning element 226 is a variable capacitor,such as a variable vacuum capacitor, having the capacitance, voltage,and frequency characteristics to be suitable for use with the low ormedium frequency supply signals required for certain ICP-facilitatedprocesses. In such implementations, the controller 228 sends the tuningsignal to the variable capacitor 226 to effect a change in thecapacitance of the variable capacitor. The resultant impedance-matchedsignal V_(L) delivered to the induction coil 206 is a function of thesupply signal V_(S) as modified by the impedance of the load as seen atthe induction coil as well as the impedance contribution from theauto-matching network 210, which is a function of the properties of thetuning element (e.g., the capacitance of a variable capacitor) 226, andin some implementations, as well as a function of the capacitance of astatic capacitor 230.

FIG. 3 shows a flowchart illustrating an example impedance matchingprocess 300. For example, the process 300 can be practiced with the ICPsystem 200 described with reference to FIG. 2. In some implementations,in block 302, the generator 208 is initialized with a frequency tuningrange and a forward power level. In one example implementation, thefrequency tuning range includes a starting or minimum frequency of 380kHz and a stop or maximum frequency of 440 kHz. In some implementations,the generator 208 is configured for both initial course tuning as wellas fine tuning after the coarse tuning is performed. For example, in oneimplementation, the course tuning is performed in tuning increments of 1kHz steps while the fine tuning is performed in, for example, tuningincrements of 100 Hz steps. In one example application, the power levelcan be approximately 2000 W. Next, in block 304, the process gas flowbegins in the ICP chamber 202. For example, the process gas used forignition can be Ar. In one implementation, there is an initial Ar burstat a chamber pressure of, for example, 50 milli-Torr (mT) to achieveplasma ignition. After ignition as the ICP chamber enters a steady-statephase, the Ar flow is lowered and the pressure in the ICP chamber isreduced to, for example, less or much less than 50 mT. In other generalapplications of the process 300, block 304 may generally signify or becharacterized by any change in the process recipe, such as from ignitionto steady-state, as just described, or such as between process steps orphases. Thus, in various embodiments, the process 300 is capable ofbeing performed, and indeed intended to be performed, in real-time andat each transition from one phase or process step to the next.

In block 306, the generator 208 generates and outputs, in forward powermode, a supply signal V_(S) having the starting frequency and thespecified power. In some embodiments, the generator 208 then begins afrequency tuning operation in block 308. In one example implementation,the frequency tuning operation of block 308 begins immediately after thegenerator 208 outputs the supply signal V_(S). As described above, insome implementations, the frequency tuning operation of block 308includes a first coarse tuning operation followed by a more fine tuningoperation when the it is determined that the coarse tuning operation hascompleted. In the coarse tuning portion of the frequency tuningoperation, the generator 208 incrementally changes the frequency of thesupply signal V_(S) in the specified increments (e.g., 1 kHz) beginningat the specified starting frequency and continuing up to a maximum atthe specified stop frequency. As the generator 208 is tuning thefrequency of the supply signal V_(S), the generator is also detectingthe reflected power in block 310. Although block 310 is shown asoccurring after block 308, it is to be understood that block 310 mayoccur simultaneously, concurrently, or otherwise in parallel with block308. In some example implementations, the generator 208 is configured tosample the supply signal V_(S) and any reflected signals at a samplingfrequency in the range of approximately 100 Hz to approximately 1 kHzduring the operation of the ICP system 200, or at least during thetuning and detecting operations of blocks 308 and 310.

In particular implementations, the generator 208 is configured tocontinue the tuning and detecting operations of blocks 308 and 310,potentially increasing the frequency of the supply signal V_(S) up to amaximum of the stop frequency, followed by potentially decreasing thefrequency of the supply signal V_(S) back down to a minimum of thestarting frequency or to a midpoint in between, and potentiallyperforming one or more additional iterations of increasing anddecreasing the frequency, until the generator 208 identifies aparticular frequency increment or range—in this example a 1 kHzrange—for which the generator detects the minimum amount of reflectedpower (all other conditions being constant). In implementations in whichthe tuning operation in block 308 includes both coarse tuning as well asfine tuning, the generator 208 can then begin iterations of fine tuningwithin the 1 kHz incremental range identified with the coarse tuningoperation. For example, as described above, such fine tuning incrementscan be 100 Hz increments. The fine tuning operation can proceed in asimilar fashion as the coarse tuning operation, but with the smaller(e.g., 100 Hz) tuning increments and within the smaller 1 kHz frequencyrange (or perhaps shortly therearound as well). The fine tuningoperation in block 308 and detection in block 310 proceeds until thegenerator 208 identifies, in block 312, a particular frequency for whichthe generator detects the minimum amount of reflected power (all otherconditions being constant).

Because many of the impedance contributions are frequency dependent, asthe generator 208 tunes the frequency of the supply signal V_(S), theimpedance of the load varies with the tuning of the frequency. Forexample, in implementations in which the tuning element 226 is orincludes a variable capacitor, as the generator 208 tunes the frequencyof the supply signal V_(S), the variable capacitor reacts to thefrequency changes and the impedance contribution from the tuning element226 changes. Because the power reflected back from the load to thegenerator 208 increases as the impedance mismatch between the generatorand the load increases, and because the impedance of the load is afunction of the frequency and often also the power of the supply signalV_(S), the generator is able to determine empirically during the tuningoperation in block 308 whether further increases or decreases in thefrequency of the supply signal V_(S) will result in more or less powerbeing reflected, and subsequently, to tune the frequency in thedirection that results in less power being reflected. In this matter,after one or more iterations, the generator 208 is able to identify, inblock 312, the frequency for which the reflected power is minimized.

By performing the tuning, detecting, and frequency identifyingoperations of blocks 308, 310, and 312, the generator 208 iseffectively, or inherently, functioning to identify the frequency of thesupply signal V_(S) that causes, or results in, the best impedancematching between the load and the generator for a given auto-matchingnetwork configuration and for a given process recipe. In particular, byperforming the tuning, detecting, and frequency identifying operationsof blocks 308, 310, and 312, the generator 208 is functioning toidentify, in real time, the frequency of the supply signal V_(S) thatcauses, or results in, the best match of the imaginary part of theimpedance (the reactance) of the load with the imaginary part of theimpedance (the reactance) of the generator. Ideally, the generator 208identifies a frequency of the supply signal V_(S) that results in acancellation of the reactance of the generator by the reactance of theload (because the impedance of the load should be the complex conjugateof the impedance of the generator when the impedances are fully matchedfor maximum power transfer). The generator 208 then sets or locks in thefrequency of the supply signal V_(S) to the identified frequency for thecurrent process step or phase.

In various implementations, after identifying or determining thefrequency that results in the best match of the reactance in block 312,the auto-matching network 210 then performs, in block 314, a secondtuning operation. In block 314, the auto-matching network 210 tunes thetuning element 226—for example, by changing the capacitance of avariable capacitor of the tuning element—in order to effect a change inthe impedance of the load. In some implementations, the auto-matchingnetwork 210 tunes (e.g., varies the capacitance of) the tuning element226 to effect a change in the real part of the impedance of the load—theresistance of the load. Ideally, the auto-matching network 210 tunes thetuning element 226 until the resistance of the load matches theresistance of the generator 208. As described above, in some exampleimplementations, such matching occurs when the phase and magnitude errorcorrection signals from the phase and magnitude detector 226 are zero.When the phase and magnitude error correction signals are zero, thecontroller 228 sends (or is already sending at that point) the tuningsignal to the tuning element 226 that results in the best matching ofthe impedance of the load to the impedance of the generator 208. Asdescribed above, the frequency tuning operation 308 serves primarily tomatch the reactance while the (e.g., capacitance) tuning operation ofblock 314 serves primarily to match the resistance.

Although block 314 is shown as occurring after blocks 308, 310, and 312,in actual practice, block 314 may begin at approximately the same timeas block 308. However, although the tuning operation of theauto-matching network may be started when block 308 begins, because theauto-matching network 210 generally includes an electromechanical tuningelement 226 or one or more other devices that take relatively longer torespond as compared with the frequency tuning, detecting, andidentifying operations of blocks 308, 310, and 312, the effect of thetuning operation of the auto-matching network 210 in block 314 may notbe realized until after block 312 is finished. This latency in theauto-matching network 210 can be exploited here to allow the tuning,detecting, and identifying operations of blocks 308, 310, and 312 tofinish before the auto-matching network effects changes in the impedanceof the auto-matching network by way of the tuning element 226. Thus,while the generator 208 is tuning the frequency of the supply signal soas to achieve the minimum power reflection, the auto-matching network ispreparing to adjust the real part of the impedance. In this sense, theauto-matching network 210 can be said to perform a “half auto-match”because it responds and adjusts the real part of the impedance only (orprimarily), and only (or primarily) after the imaginary part of theimpedance is adjusted by the generator 208. In some implementations, anintentional delay is actually introduced between when the frequencytuning operation of block 308 begins and when the auto-matching tuningoperation of block 314 begins. Such a delay can be intentional set bydelaying, adjusting, or slowing one or more control signals such asthose used to control the electromechanical elements of theauto-matching network 210. This ensures that the frequency tuningoperation of block 308 can complete prior to the start of theauto-matching tuning operation of block 314.

As described above, in some implementations, the process 300 isperformed during or immediately after any change in the process recipe.In this way, various embodiments provide real-time impedance matching ofboth the imaginary (reactance) component, solely or primarily by way offrequency tuning in the generator 208, as well as the real (resistance)component, solely or primarily by way of the auto-matching network 210,during or immediately after any process step or other phase transitionin a single or multi-process step ICP plasma-facilitated treatment.

Using the aforementioned process 300 in conjunction with anauto-matching network (such as auto-matching network 210) and agenerator (such as generator 208) configured to output a 2000 W supplysignal V_(S) in forward power mode, the inventors have achieved lessthan 1% reflected power (e.g., less than 15 W). Specifically, theinventors have achieved a reflected power that reaches a maximum of 6 Wduring process step transitions using a supply signal V_(S) generatedwith a frequency of 405.9 kHz at 1999 W forward power.

While the process 300 described above was described as having aparticular frequency tuning range—a starting frequency of 380 kHz, astop frequency of 440 kHz, and coarse and fine tuning increments of 1kHz and 100 Hz, respectively—other frequency ranges and tuningincrements may be desirable or even required in other applications. Onereason for pre-identifying a tuning range is that the ICP generatorsgenerally have multiple resonance points. If the generator reaches oneof these resonance points during the frequency tuning operation in block308, the generator (e.g., the control loop of the generator) may becomelost and not be able to iteratively identify the frequency for whichminimum power reflection is achieved. Thus, before process 300 isperformed, appropriate boundary conditions (e.g., the starting and stopfrequencies) may desirably be determined such that the generator willnot tune the frequency below a specified starting frequency or above aspecified stop frequency to ensure that the frequency tuning operationdoesn't encompass tuning near or over such resonance points. Generally,the boundary conditions will vary be application (e.g., process recipe).In one example implementation, a network analyzer is used to identifythe impedances of the resonance points that are to be avoided such thatthe generator is able to identify and lock onto a frequency for whichminimum power reflection occurs.

FIG. 4 shows a flowchart illustrating an example initialization andsynchronization process 400. The process 400 can be performed, forexample, by a user at various times such as, for example, whenconfiguring a generator 208 with a particular ICP system 200. In someimplementations, the process 400 begins without the generator 208connected. In block 402, with the generator 208 still unconnected, anetwork analyzer is connected to the ICP system 200 and a frequencyrange is set for the network analyzer. Next, in block 404, the networkanalyzer is calibrated. In some implementations, the process thenproceeds in block 406 with the network analyzer performing a networkanalysis 406 without the auto-matching network 210 connected. Duringblock 406, the network analyzer identifies the resonance points and asuitable tuning frequency range for the generator 208. After this“course” identification of the resonance points and a suitable tuningrange, the network analyzer may then be used to perform a subsequentnetwork analysis in block 408 with the auto-matching network 210connected. With the auto-matching network 210 connected, the networkanalyzer can more closely identify the resonance points in block 410 andto more closely identify and define a suitable tuning frequency rangefor the generator 208 in block 412, including, for example, anappropriate starting frequency, an appropriate stop frequency, andtuning increments, etc.

Additionally, because the auto-matching network 210 must be able torespond to the tuning frequency of the generator 208 during thefrequency tuning operation described above in block 308, the tuningfrequency of the generator is limited by the response speed of thematching network 210. Thus, in some instances, the accuracy of thetuning operation may be limited by the response speed of the matchingnetwork. For example, if the tuning operation is being performed fasterthan the matching network can respond accurately, the frequency tuningoperation can erroneously proceed in the wrong direction (e.g., awayfrom the frequency that would achieve the lowest reflected power) andthe system may, in some instances, either not recover or takesignificant time to recover. Thus, one or both of blocks 406 and 408 caninclude one or more initial iterations of one or more coarse frequencytuning operations and one or more fine tuning operations at one or moretuning speeds to determine a safe or maximum tuning speed to be used inthe tuning operation 308 to ensure a suitable responsiveness of theauto-matching network 210, as well as to define a tuning range that willoptimize the ability of the generator 208 and auto-matching network 210to best match the impedance of the generator with the impedance of theload to be supplied by the generator. Generally, the boundary and otherconditions will vary with the application and particular customerprocess recipe. Each of blocks 406 and 408 may also include one or moreiterations of one or more frequency tuning operations for one or moreprocess stages (e.g., ignition and steady-state) as well as in betweenprocess stages of various multi-step recipes.

Additionally, an intentional delay required or desired between the startof the frequency tuning operation and the start of the auto-matchingtuning operation, described above with reference to process 300, alsocan be determined in block 414 based on, for example, the tuningoperations in blocks 406 and 408. In some implementations, a startingimpedance of the tuning element in the auto-matching network 210 can bedetermined in 416. The starting impedance also can be used forcontrolling the delay between the generator's frequency tuning operationand the tuning operation performed by the auto-matching network 210. Forexample, by selecting an appropriate starting impedance, an inherentdelay associated with the starting impedance can be introduced betweenthe frequency tuning operation and the auto-matching tuning operation.Any or all of these parameters or other information can then be providedto a user such as a customer so that they may better optimize theprocess 300 described above.

Another aspect of the invention is an apparatus configured to accomplishthe methods described herein. A suitable apparatus includes hardware foraccomplishing the process operations and a system controller havingsoftware or other computer-readable instructions for controlling processoperations in accordance with the present invention. For example, thesystem controller may control one or more of the hardware components ofICP system 200 shown in FIG. 2. Specifically, the system controller mayenable automated or user control of the generator 208, the auto-matchingnetwork 210, and other components of the ICP system 200. In someimplementations, the system controller may include the controller 228described above or, additionally or alternatively, may itself controlthe controller 228 described above. The system controller will typicallyinclude one or more memory devices and one or more processors configuredto execute the instructions so that the hardware—such as the generator208, auto-matching network 210, and other components of the ICP system200—will perform a method in accordance with the present invention.Machine-readable media containing instructions for controlling processoperations in accordance with the present invention may be coupled tothe system controller.

As described above, the apparatus and processes described above may beused in conjunction with lithographic patterning tools or processes, forexample, for the fabrication or manufacture of semiconductor devices,displays, LEDs, photovoltaic panels and the like. Typically, though notnecessarily, such tools or processes will be used or conducted togetherin a common fabrication facility. Lithographic patterning of a filmtypically comprises some or all of the following steps, each stepenabled with a number of possible tools: (1) application of photoresiston a workpiece, i.e., substrate, using a spin-on or spray-on tool; (2)curing of photoresist using a hot plate or furnace or UV curing tool;(3) exposing the photoresist to visible or UV or x-ray light with a toolsuch as a wafer stepper; (4) developing the resist so as to selectivelyremove resist and thereby pattern it using a tool such as a wet bench;(5) transferring the resist pattern into an underlying film or workpieceby using a dry or plasma-assisted etching tool; and (6) removing theresist using a tool such as an RF or microwave plasma resist stripper.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe appended claims. It should be noted that there are many alternativeways of implementing the processes, systems and apparatus of the presentembodiments. Accordingly, the present embodiments are to be consideredas illustrative and not restrictive, and the embodiments are not to belimited to the details given herein.

1-20. (canceled)
 21. A system comprising: a plasma system including areaction chamber and an induction coil around the reaction chamber; agenerator to generate a supply signal to power the induction coil for aplasma-facilitated process; and an auto-matching network to receive thesupply signal and to provide the supply signal to the induction coil ofthe ICP system; the generator further to detect a reflected power signalfrom the plasma system, and tune a frequency of the supply signal to atuned frequency for which the power of the reflected power signal isapproximately minimized; and the auto-matching network further todetermine a phase and magnitude of the supply signal at the tunedfrequency, determine a phase and magnitude of a reflected power signalfrom the plasma system, and tune an impedance of the auto-matchingnetwork to an impedance for which the differences in the determinedphases and magnitudes, respectively, of the supply signal and thereflected power signal are approximately minimized.
 22. The system ofclaim 21, wherein the generator is configured to generate the supplysignal in a forward power mode.
 23. The system of claim 21, wherein thesupply signal is a radio frequency (RF) signal, and wherein thegenerator is configured to generate the supply signal at a frequencybelow 1 MHz.
 24. The system of claim 23, wherein the generator isconfigured to tune the frequency of the supply signal within a rangethat starts at approximately 380 kHz and which stops at approximately440 kHz.
 25. The system of claim 21, wherein the auto-matching networkincludes a phase and magnitude detector configured to: determine thephase and magnitude of the supply signal at the tuned frequency;determine the phase and magnitude of the reflected power signal from theplasma system; and generate phase and magnitude error correction signalsbased on the differences in the determined phases and magnitudes,respectively, of the supply signal and the reflected power signal. 26.The system of claim 25, wherein the auto-matching network furtherincludes a controller configured to: receive the phase and magnitudeerror correction signals; and generate a tuning signal based on thephase and magnitude error correction signals.
 27. The system of claim26, wherein the auto-matching network includes at least one tuningelement having an impedance based on the tuning signal.
 28. The systemof claim 27, wherein the tuning element includes a variable capacitorhaving a capacitance based on the tuning signal.
 29. The system of claim21, wherein the generator tunes the frequency of the supply signal tothe tuned frequency and the auto-matching network tunes the impedance ofthe auto-matching network in real time.
 30. The system of claim 21,wherein the generator tunes the frequency of the supply signal to thetuned frequency and the auto-matching network tunes the impedance of theauto-matching network during each transition between process steps of amulti-step process.
 31. A method comprising: generating, by a generator,a supply signal to power an induction coil of a plasma system for use ina plasma-facilitated process; detecting, by the generator, a reflectedpower signal from the plasma system; tuning, by the generator, afrequency of the supply signal to a tuned frequency for which the powerof the reflected power signal is approximately minimized; receiving, byan auto-matching network, the supply signal at the tuned frequency;determining, by the auto-matching network, a phase and magnitude of thesupply signal at the tuned frequency; determining, by the auto-matchingnetwork, a phase and magnitude of a reflected power signal from theplasma system at the tuned frequency; and tuning, by the auto-matchingnetwork, an impedance of the auto-matching network to an impedance forwhich the differences in the determined phases and magnitudes of thesupply signal and the reflected power signal are approximatelyminimized.
 32. The method of claim 31, wherein the supply signal isgenerated in a forward power mode.
 33. The method of claim 31, whereinthe supply signal is generated at radio frequencies (RF) below 1 MHz.34. The method of claim 33, wherein the generator is configured to tunethe frequency of the supply signal within a range that starts atapproximately 380 kHz and which stops at approximately 440 kHz.
 35. Themethod of claim 31, further including generating phase and magnitudeerror correction signals based on the differences in the determinedphases and magnitudes, respectively, of the supply signal and thereflected power signal.
 36. The method of claim 35, further including:receiving, by a controller, the phase and magnitude error correctionsignals; and generating, by the controller, a tuning signal based on thephase and magnitude error correction signals; and adjusting an impedanceof a tuning element of the auto-matching network based on the tuningsignal.
 37. The method of claim 36, wherein the adjusting the impedanceof the tuning element includes adjusting the capacitance of the tuningelement.
 38. The method of claim 31, wherein the frequency of the supplysignal and the impedance of the auto-matching network are tuned in realtime.
 39. The method of claim 31, wherein the frequency of the supplysignal and the impedance of the auto-matching network are tuned duringeach transition between process steps of a multi-step process.
 40. Themethod of claim 31, further including performing a network analysisoperation to identify one or more resonance points that should not betuned to or tuned over during the tuning of the frequency of the supplysignal.